For example, among various sorts of brushless driving motors, there are those in which, in order to make current flow in good timing through driving coils of different phases, depending on the rotational position of the rotor magnet, Hall elements for detecting magnetic poles of the rotor magnet are used. The conduction timing of the driving coils of different phases can then be determined on the basis of the detection signal obtained by these Hall elements.
FIG. 8 illustrates a prior art example of such a magnetic pole detecting Hall element, in which a Hall element chip 65 is secured to a bridge-shaped holder 67. The two extremity portions of holder 67 are bent so as to form leg portions 68 so that the magnetic field sensitive surface 66 of chip 65 is parallel to the front surface of the holder 67. The holder 67 is secured to e.g. a predetermined circuit pattern, etc. on a wiring board 69 with the leg portions 68 of the two extremity portions of the holder 67 being secured so that the magnetic field sensitive surface 66 stated above is also parallel to the board 69. The magnetic field sensitive direction of the Hall element is the direction which is perpendicular to the magnetic field sensitive surface 66 as indicated by an arrow in FIG. 8. Consequently, it can detect only the magnetic pole generating a magnetic flux perpendicular to the wiring board 69.
The prior art magnetic pole detecting Hall element is suitable for detecting the magnetic pole by locating it face to face with a flat magnet such as those in a face-to-face type brushless motor, because the magnetic field sensitive direction is perpendicular to the surface on which the Hall element 65 is mounted, i.e. the surface of the wiring board 69. On the contrary, in a magnet in which magnetic poles are arranged along the periphery of a cylinder, even if it is tried to detect the magnetic poles by locating Hall elements face to face with the peripheral surface of the magnets, it is not possible to detect the magnetic flux, because the magnetic flux passes parallely to the magnetic field sensitive surface 66 of the Hall elements. Further, since the holder 67 has no reference for use in positioning it with respect to the wiring board 69, the precision of the mounting position is not good and it is not possible to detect the magnetic pole with a high precision. As the result, there is a problem that the efficiency of the motor is lowered.
In order to solve this problem, a technique has been adopted, by which the Hall element is mounted so as to be perpendicular to the magnetic field sensitive surface, as disclosed in JP-Utility Model-A-59-34492. However, since the Hall element 14 is positioned by means of a positioning plate in the Utility Model A-59-34492, the mounting and the regulation of the Hall element are very troublesome and the number of parts increases. Another sensor holder is disclosed in JP-Utility Model A-62-20313, on which an MR sensor, a kind of magnetic field sensitive element, is mounted. However, in this sensor holder also the holder and the sensor are constructed separately from each other. In addition, the mounting of the sensor is effected by passing a screw pass through an elongated hole formed in the holder so that the positional regulation can be effected together with the fixing operation.